For this you have to beat Stage 3 Day 1 to get the Ancient Buckle. This item enables Arma-mode, which allows Dillon to become invincible and do triple damage to enemies.
Unlock Sal's Hut
Complete the game once and collect every star (50) in the game
Heart Shard That I Know
You must go to the ancient ruins on the top of the cliff on Village One and any day if it doesn't change by day. I think you have to spin until it opens and it might get a health power up if you get the other one.